Coupled Subsurface and Surface model: A Case Study

An integrated model that couples surface and subsurface models was developed for a huge carbonate oil reservoir overlain by a large gas-cap located in the Middle East region. The main objective of the integrated model is to quickly evaluate changes in production strategy and provide more accurate forecast of field performance than with conventional approaches where surface and subsurface performance are evaluated separately. Building a fully integrated model is a very challenging task, due to the complex nature of the field process, including compositional variations, NGL processing and evaluation of gas disposition options. The surface network model was developed to allow evaluation of liquid and gas velocity in the flowlines and trunklines, and erosional velocity and back pressure to every well in the network. Trunklines were modeled with detailed elevation profiles to capture the complex nature of desert terrain found in the field. The subsurface model is a huge resolution model with more than 60 million grid-cells. The reservoir simulation model is compositional, having nine-components and runs on a state-of-the-art in-house simulator, GigaPOWERSTM. This paper highlights the process in building the fully coupled model by a multidisciplinary team, including the subsurface model, wellbore models, surface network model, and the integration layer between those different standalone models. The paper also discusses the issues encountered during building the integrated model and how those challenges were resolved.